1. Field of the Invention
The present invention relates to a flow machine with rotor and stator in a single-stage or multi-stage embodiment in flow-oriented terms. More specifically, the present invention relates to a flow machine whose rotor comprises moving blades and whose stator comprises a housing with guide vanes, whereby the guide vanes are arranged as at least one guide vane ring with a radially inner and a radially outer cover band, such as an axial low-pressure turbine.
2. Description of the Prior Art
For example, German Letters Patent 27 45 130 discloses such a flow machine, whereby this patent specifically relates to axial turbines with labyrinth seals. The flow channel of the working agent leads alternately through vane rings and moving blade rings, whereby the static component parts project thereinto radially from the outside and the rotating component parts project thereinto radially from the inside. As FIG. 1 of said patent clearly shows, there are both radially inwardly arranged seals between the rotor and the vane rings (inner air seal) as well as radially outwardly arranged seals between the moving blades and the stator (outer air seal).
Given the axial turbine according to German Letters Patent 27 45 130, the sealing fins (reference numeral 8) of the inner air seal are secured to the rotor (reference numeral 4), so that their dimensions or, respectively, dimensional deviations are dependent on the conditions at the rotor (temperature, speed). By contrast thereto, the appertaining seal coat (reference numeral 7) is secured to the inner cover band (reference numeral 20) of the guide vane segments (reference numerals 1, 5). The guide vane segments are seated at the housing (reference numerals 13, 14), so that the dimensions or, respectively, dimensional deviations of the seal coat are ultimately significantly co-determined by the conditions outside at the housing. The conditions at the rotor, on the one hand, and at the housing, on the other hand, often change neither conformally nor isochronically, so that gap-modifying relative movements between the seal elements (reference numerals 7, 8) derive. The same is true of the outer air seal (reference numerals 11, 12). The specific type of vane ring fastening at the housing is employed thus or comparably given larger engines. Each segment of a vane ring is seated as mechanical unit at housing elements (reference numeral 14) having a hook-shaped longitudinal section that are annularly closed in circumferential direction. At the upstream end of the outer cover band, each guide vane segment comprises an edge bead with channel that embraces the hook-shaped housing element (reference numerals 14, 22) claw-like (see FIG. 3). At the downstream end of the outer cover band of each guide vane segment, a seating unit that is angled-off in longitudinal section is present with a radially outwardly directed seating surface that is pressed against the corresponding hook-shaped housing element during operation as a result of a flow induced tilting moment around the upstream "claw bearing" (see FIG. 1). Due to the hook-shaped housing elements--which can also be referred to as "hook rings"--, high-density heat flows flow to the colder housing, whereby the "hook rings" are increasingly plastically deformed due to creeping, specifically in the region of the "claw bearings". Only a permanent cooling of the "hook rings" can usually alleviate this situation. If present, an active clearance control system (ACC) can be co-utilized, but this must then be in permanent operation.
German Letters Patent 35 40 943 discloses such a clearance control system specifically for a ducted-fan turbine engine. Given this, the secondary air channel extends at least to the end of the turbine region and comprises openings (reference numeral 11) in its inside wall through which secondary air can be designationally blown onto regions of the turbine housing from the outside. Given this simplified ACC system, there is the potential problem that the slight over-pressure of the secondary air stream is inadequate for generating cooling air streams with adequate mass throughput in topically tightly limited housing zones due to correspondingly small flow crosssections. In an active clearance control, compressor air from the booster or, respectively, low-pressure compressor is usually branched off as coolant, conducted in separate channels and designationally blown out via valves.
In smaller gas turbine engines, it is known to implement vane rings as self-bearing, integral component parts with closed cover bands and to center them in the housing. This "monolithic" solution is limited to blade rings with relatively small dimensions for manufacture-oriented as well as strength-oriented reasons (thermal stresses).
German Published Application 33 36 420 discloses a mechanism for protection against an over-turning of a gas turbine rotor given shaft fracture. The mechanism works in such a way that the guide vane segments of at least one vane ring are axially pivoted and brought into contact/engagement with neighboring guide vanes. The mutual mechanical blade friction and destruction quickly and effectively brakes the rotor. The guide vane segments belonging to the mechanism each respectively comprise a drag bearing at the outer cover band segment and have their inside circumference connected with an interlocking, ring-like reinforcing element, so that, together, the segments form a rigid, self-bearing vane ring. Given the embodiment according to FIGS. 2 and 3, the drag bearings (reference numerals 36, 56, 58 and 64) form a spoke centering for the self-stable vane ring, which enables an exact positioning/centering given reduced thermal stresses. The heat transmission from the hot gas zone to the housing (reference numeral 34) is disadvantageous, the bearing elements also being affected by this. The resulting high temperatures and temperature gradients in the component parts of this region can considerably shorten the service life.
U.S. Pat. No. 3,588,267 discloses a vane ring design implemented in plastic wherein the blades are secured to a closed, inner torus and form a self-bearing ring with this. The outer blade tips are implemented without cover band and are glued directly in recesses of a metallic housing, whereby the elasticity of the gluing compensates/absorbs minor relative dislocations. It is obvious that this design is completely unusable for higher temperatures and can at best be employed in the fan or, respectively, low-pressure compressor area.
In view of these known solutions and their disadvantages, objects of the present invention include creating a flow machine with rotor and stator as well as with at least one vane ring comprising a respective outer and an inner cover band that is distinguished in all operating conditions by an optimum clearance retention, i.e. by especially low leakage losses that vary little and can be computationally well-acquired, thus, a high efficiency, as well as by a relatively simple, cost-beneficial and weight-beneficial, durable and maintenance-friendly design without requiring an active clearance control system (ACC) and can be implemented with high powers and dimensions and is also functionally rugged.